It is generally known that, during charging processes such as softening or demineralization of aqueous solutions, the ion exchanger materials, such as bead-like ion exchange resins, accept ionogenic dissociation components of the dissolved salts, such as calcium ions, and release the ions stored in the active centers of the ion exchange material, such as sodium ions, into the aqueous solution. When the supply of stored ions is depleted--i.e., in this example, when all stored sodium ions are exchanged for calcium ions--the ion exchange stops. In order to regenerate the ion exchange material, a solution of the ions stored, e.g , a sodium chloride solution, is passed through the ion exchange materials bed, and the ions accepted by the exchanger during charging, i.e , the calcium ions, are eluted, and the sodium ions supplied from the regenerating agent are placed back onto the active sites of the ion exchange material.
To conduct regeneration following charging in the downward direction, it is known to feed the regenerating solution from top to bottom, i.e., in a co-current direction, through the ion exchanger. The regeneration of the ion exchange bed in a co-current direction has considerable drawbacks, as illustrated by the example of the softening of hard water. In this case, hard water flows through layers of ion exchanger material (such as ion exchange resins) in a filter container, and the exchanger becomes charged in the flow direction, i.e., from top to bottom, with calcium ions. The lower the concentration of calcium ions in the lowermost ion exchange layer, which is the last one through which the water to be treated flows, the lower the residual hardness in the product water, i.e., the better the quality. During the subsequent regeneration in a co-current system, the calcium ions highly enriched in the upper ion exchanger layers are eluted from the resin by the regenerating solution and washed into the lower layers. In order to confer to these lower layers a good state of regeneration, the entire ion exchanger must be treated with a large excess of regenerating agent. These excess amounts are not fully utilized and represent a major economic loss. Furthermore, these excesses get into the sewage and increase the salt levels in the sewers. The excess sodium and chloride ions of the unused regenerate are environmentally detrimental.
It is also known to run the regenerant solution in the direction opposite to the charging direction, i.e., in an upward or countercurrent direction, through the ion exchanger. the disadvantage of this process is that the entire bed of ion exchange material is turned over and mixed together In particular, the ion exchange resins highly charged with calcium ions are forced from the upper layers to the lower layers, and the ion exchange material that is still largely uncharged is forced upward from the lower layers. Thus, because of this rearrangement, the entire ion exchange bed must be treated with a large excess of regenerant in order to achieve good product quality. The unused regenerant portion enters the sewers as highly salinated waste water and is also a major burden to the environment. If regeneration is conducted, for example, with 200% of the theoretical amount, twice as much regenerant--sodium chloride in the case of water softening--enters the sewage during each cycle than would be theoretically necessary.
It has now been found that the most efficient use of regenerant and, at the same time, the best product quality is obtained when the ion exchange materials are not mixed or rearranged during the regenerative treatment cycle with upward flow. In known systems, attempts have been made to control the mixing either by physical restraints or by blocking flow from the top. Each of these attempt has its own known drawbacks and operational problems.
Accordingly, it is the object of the present invention to overcome the aforesaid problems associated with regenerating layered beds ion exchange materials, such as ion exchange resins.
Specifically, it is the object of the present invention to achieve the regeneration with substantially less regenerating agent thereby obtaining a substantial saving in regenerant costs. It is a further object of the present invention to regenerate the ion exchange materials with substantially less regenerating agent discharging to waste, thus substantially reducing the detriment to the environment.